1. Field of the Invention
This invention pertains in general to the field of anesthetic breathing apparatuses. More particularly the invention relates anesthetic breathing apparatuses having improved monitoring of anesthetic agents.
2. Description of the Prior Art
Anesthetic breathing apparatus are known. For instance in WO2007/071756 of the same applicant as the present application, various set-ups of anesthetic breathing apparatus are disclosed. An anesthetic gas monitor is normally provided for monitoring a concentration of an anesthetic agent delivered to a patient from the anesthetic breathing apparatus.
Anesthetic breathing apparatuses, such as disclosed in WO2007/071756, conventionally comprise a single gas monitor providing, amongst others, a concentration of anesthetic agents and other gas components, usually in a breathing circle of the anesthetic breathing apparatus. The monitored concentration is conventionally a parameter presented to the operator of the anesthetic breathing apparatus for controlling and perhaps managing adjustments of anesthesia performed by means of the anesthetic breathing apparatus.
It might be an issue causing deteriorated operation of the anesthesia when the single gas monitor is not working properly. For instance, when the gas monitor is out of calibration, the patient might be provided with unintended high or low concentrations of an anesthetic agent due to erroneous adjustments of the anesthetic breathing apparatus.
An anesthetic breathing apparatus having a single anesthetic gas monitor with improved safety is disclosed in EP1140264A1 of GE Healthcare. A feedback control system is provided, which periodically compares a measuring value obtained from a fresh gas sample with a real reference value of the sample, based on which required safety measures are taken. This means both that a calibration is done at defined time intervals and that a real and known reference value has to be present in the system. At least the latter is difficult to provide in practice as a reference value may also be erroneous.
Also, when having fast responsive anesthetic vaporizers of the injector type, these need to be controlled by a feedback loop that is based on a real time measurement of delivered anesthetic agent concentration. In case the measurement of the concentration of the anesthetic agent fails in this control loop, erroneous concentrations may be delivered by the anesthetic vaporizer.
An anesthetic breathing apparatus having two anesthetic gas monitors is disclosed in US2005/0103338A1 of Dräger Medical AG. A first gas monitor is connected to the trailing side of a mixing chamber volume in a ring line and a second gas monitor is connected to a patient connection. A plausibility comparison between the measured values of the first gas monitor and the second gas monitor is made.
However, the system does not take into consideration that the actual concentrations at the two different measurement points of the two different anesthetic gas monitors may be different. Also, the system may shut down delivery of anesthetic agent of the patient during surgery even if the concentration of anesthetic agent delivered to the patient is correct, e.g. in case a sample line of one of the two anesthetic gas monitors is clogged and thus measurement values are wrong.
Hence, an improved anesthetic breathing apparatus would be advantageous and in particular allowing for increased operational safety and/or patient safety would be advantageous.